That would be a good solution. Remember though that manyshot was added because ranged was admittedly underpowered at upper levels. It does not compensate, except for those 20 seconds out of 140 (1/7 of the time) for the underpowering, at present. It has its expense in ammunition, too. Suppose you trigger it and the fight ends, you can't end it, to save the timer or the ammunition, presently.
The real solution is to make it a stance, only preserved while immobile. Help with the strafing advantage, though repeating crossbows could still do it.
Special note: I play both sides of this issue and know the differences. I stress again that Longbows in particular are at the bottom of the food chain at higher levels. (I have two clerics, a wizard, a sorcerer, a rogue, a ranger, and a multi ro/pa/fi that has manyshot. Not a one of them below level 10.)